Hello and thank you for posting!
I am sorry things are not working as expected while using your new Plugable UD-3900 docking station and I would be happy to help.
We have encountered rare cases where a USB printer (especially a ‘multi-function’ printer like yours) may not work as expected when connected to the dock due to how the printer’s software driver works.
To expand further, if the printer driver was installed when the printer was directly connected to a USB port built-in to the laptop the printer may not be recognized by the printer driver when it is later connected to an external USB hub of any kind (not just our dock).
Uninstalling the printer software provided by the printer manufacturer and then reinstalling can often help.
As a first step, I would recommend disconnecting the printer from your setup. I would then recommend completely uninstalling the Epson software driver for the printer on your system, and then rebooting your laptop.
Once rebooted, please re-install the Epson software driver and when doing so connect the printer to the UD-3900 docking station to see if that changes the behavior.
Apologies again for the frustration, and please let us know if that information helps!